Display devices for viewing a virtual image of a display are described in U.S. Pat. No. 3,170,979 to Baldwin et al. and U.S. Pat. No. 3,059,519 to Stanton. These devices are complex and expensive and are intended for use by pilots and other professionals who need to have certain information continuously displayed within their line-of-sight.
The Baldwin et al. device superimposes an image from a cathode ray tube onto a half-silvered, see-through mirror positioned in the viewing field of the user so as to superimpose an image of the tube display on the normal background environment of the viewer. An elongated tube contains the cathode ray tube and a plurality of separate lenses which project the image onto a half-silvered surface and focus the image at optical infinity. The device is mounted on a harness worn over a helmet and measures about 11/4.times.5 inches and weighs less than six ounces.
The Stanton device includes a cathode ray tube and a plurality of lenses and mirrors. The Stanton device is mounted on the inside of a helmet and the image is displayed on a full reflecting mirror positioned at the lower edge of the helmet just above the pilot's eyes.
The Baldwin et al. and Stanton devices are complex optical systems including a plurality of separate lenses and mirrors which must be accurately positioned within the composite assembly. Each device is sufficiently large that it must be mounted on a helmet to provide sufficient stabilization and support. The price of these complex units can be justified when purchased for use by a pilot or other professional, but they are not intended for sale as a consumer item.
It has been suggested to provide a lap counter on a pair of swimming goggles in U.S. Pat. No. 4,530,105 to Rabinowitz. The counter includes a flux change detector which detects a change in direction of the earth's magnetic field when the swimmer changes direction, means for producing a pulse output during each such change in direction, circuit means for counting the pulses, and display mean for displaying the number of laps completed, such as an LED or LCD display. An LED display is shown mounted on one lens of the goggles with battery-operated circuitry for the display mounted on the headband of the goggles. Rabinowitz does not disclose an operative device because no means are described for focusing the display or rendering it waterproof. An LED display device mounted on a pair of swimming goggles is too close to the viewer's eyes to be readable.
It is an object of this invention to provide a periscopic display device for close up viewing of a virtual-image display.
Other objects are to provide a periscopic display device which is lightweight, inexpensive to produce, waterproof, dustproof, impact-resistant, and adapted to be mounted on the headwear of the viewer.